1. Field of the Invention
This invention pertains to a process for preparing colorable chromogenic compounds eligible for use in pressure-sensitive record material and to the compounds themselves. Pressure-sensitive mark-forming record systems, single sheet and manifold, are improved by use of these compounds.
More specifically, this invention relates to chromogenic compounds which have the form of substantially colorless or slightly colored solids, or which approach being colorless when in liquid solution; but, which may be converted to dark-colored forms upon reactive contact with acidic material. As used in mark-forming systems, marking in desired areas on support webs or sheets may be accomplished by effecting localized reactive contact between the chromogenic material and the acidic material on or in such web or sheet, such material being brought thereto by transfer, or originally there, in situ. The desired reactive contact forms dark-colored materials in the intended image-marking areas.
The chromogenic compounds of this invention have the following general structure: ##STR2## R can be, among several others, hydrogen, alkyl, cycloalkyl, halo, alkoxy, and aryl, substituted or unsubstituted; and E is a broad family of aromatic structures.
2. Description of the Prior Art
Several phthalide and fluoran chromogenic compounds and processes for preparing them have been disclosed. For example, U.S. Pat. No. 3,491,111, issued Jan. 20, 1970, discloses indol- and carbazol-substituted phthalides. U.S. Pat. No. 2,417,897, issued Mar. 25, 1947, discloses crystal violet lactone. U.S. Pat. No. 3,681,390, issued Aug. 1, 1972, discloses aryl-substituted fluorans.
U.S. Pat. No. 3,672,935, issued June 27, 1972, discloses use of colorless chromogenic compounds in pressure-sensitive record material.
G. Hallas, in the Journal of the Society of Dyers and Colourists, in September, 1967 at pages 368 to 373 and in June, 1970 at pages 237-242, discusses the effects of extended conjugation on colored dye compounds.